In recent years, vehicles have widely employed depress-type switches for turning on/off the brake light in brake-pedal operations. In this type of switch, the brake light turns on when depressing force is exerted on the brake pedal and the light turns off when the force is removed.
Such a conventional switch will be described hereinafter with reference to FIG. 12.
FIG. 12 is a section view of a conventional switch for a vehicle. The switch, as shown in the drawing, has case 1 with substantially a top-open box shape and actuating unit 2, both of which are made of insulating resin. Case 1 has a plurality of fixed contacts 3. Terminal sections 3A of fixed contacts 3 extend out from the bottom of case 1.
Spring 5 is placed, under a slight compression, between the bottom of case 1 and conductive metal-made movable contact 4. The resilient force of spring 5 pushes movable contact 4 upward so that movable contact 4 makes contact with fixed contacts 3. In this way, fixed contacts 3 are electrically connected via movable contact 4.
Coil-shaped returning spring 6 is disposed, under a slight compression, between the lower section of actuating unit 2 and the bottom of case 1 so as to urge actuating unit 2 upward.
Cover 7, which covers the top opening of case 1, has hollow cylinder 7A that extends upward. Operation shaft 2A of actuating unit 2 is inserted in hollow cylinder 7A so as to have vertical movement. The top end of operation shaft 2A protrudes beyond the top end of hollow cylinder 7A. The conventional switch for a vehicle is thus completed.
Such structured conventional switch is usually disposed before the brake pedal, with operation shaft 2A of actuating unit 2 depressed by an arm or the like. At the same time, terminal section 3A of fixed contacts 3 is connected by a connector or the like to an LED of the brake light.
Under the condition where a driver does not step on the brake pedal, operation shaft 2A of actuating unit 2 in a depressed state keeps spring 5 and returning spring 6 in compression, allowing movable contact 4 to move away from fixed contacts 3. Fixed contacts 3 have no electrical connection therebetween and therefore the brake light turns off.
When a driver steps on the brake pedal, the arm moves away from operation shaft 2A and therefore no depressing force exerts on the springs. The spring-back force of returning spring 6 pushes actuating unit 2 upward; at the same time, spring 5 urges movable contact 4 upward, allowing contact 4 to make contact with fixed contacts 3. Fixed contacts 3 have electrical connection and therefore the brake light turns on.
In recent years, such a brake light is often formed of an LED and a voltage of 12 V DC and a current ranging from 0.5 A to 2A is fed to the LED. Each time the contact between movable contact 4 and fixed contacts 3 is made and broken, a weak arc discharge occurs. The arc discharge causes oxide and carbide on the contact surface.
Such an arc discharge, since caused by a relatively small voltage and current, does not have enough energy for remove the oxide and carbide on the contact surface. As the switching operations between the fixed contacts and movable contact are repeatedly carried out, the aforementioned unwanted substances easily accumulate on the surface.
In the prior art, for example, Japanese Patent Unexamined Publication No. 2006-147552 disclosed a conventional switch relating to the invention.
As described above, when such an LED switch for controlling an electric circuit that carries a relatively small voltage and current, oxide and carbide easily accumulates on the contact surface. This can cause a poor contact between movable contact 4 and fixed contacts 3.